Arguably the most best option, Verbix.com is a non-profit site that includes useful features for conjugating verbs in a hundred-odd languages, from Afrikaans to Vulgar Latin (Eastern.)
The main feature is the online conjugator itself, where you plug in the infinitive of the verb you wish to conjugate and receive an impressive, if somewhat intimidating, array of the verb's various conjugated forms. It's a fantastic tool, whether you're only just learning a language or a fluent speaker who can't quite remember where to put that accent in the imperfect subjunctive.
They've got other cool features, too, including a “verb finder" and “language guesser" that will attempt to puzzle out the language from any input you provide. Their VerbWiki provides some background for the languages and also some of the logic (or lack of) behind the verbs. They also offer free and paid versions of their software for download.
Be warned: this site does not instruct you on how to properly utilize the verb once conjugated within the context of a sentence structure. Nor does it inform you, for example, of the substantial semantical differences in a subtle change of helping verbs. Verbix, like the other verb conjugating sites featured in this review, is one of many tools to be utilized in communication in foreign languages.